1. Field of the Invention
The present invention relates to continuous flow centrifuge apparatus and, more particularly, to apparatus for minimizing heat transfer from a vacuum bushing to a sample in a continuous flow centrifuge apparatus.
2. Description of the Prior Art
Continuous flow or zonal centrifugation has become an increasingly important analytical tool in the investigation of the nature of numerous biological and other chemical substances. A typical continuous flow centrifuge apparatus includes an outer housing defining a vacuum chamber which serves to enclose a rotor and a drive means therefor. The top of the outer housing supports an inlet/outlet assembly for conducting a sample solution to and from a rotary transfer tube which is connected to the rotor. A vacuum seal is formed around the transfer tube, thereby sealing the chamber.
Typically, in continuous flow centrifugation, a sample solution is continuously pumped, via the transfer tube, through the rotor cavity, which is filled with an appropriate density gradient solution. During centrifugation, the particles of interest disperse in a radial direction throughout the density gradient solution and, at equilibrium, are suspended in the solution at a location wherein their respective buoyant densities correspond to that of the solution. When equilibrium is reached, the particles of interest are removed from the rotor by displacing from the rotor cavity the density gradient solution containing the centrifuge particles by means of a liquid having a density greater than the highest density portion of the density gradient solution. A complete, continuous flow centrifuge apparatus including a method for removing the particles of interest from the rotor cavity is disclosed in U.S. Pat. No. 3,498,531 for Continuous Flow Ultracentrifuge and assigned to Beckman Instruments, Inc., the assignee of the present application.
Typically, the vacuum seal around the rotary transfer tube is created by an oil-filled bushing surrounding the transfer tube for creating an oil film between the outer surface of the transfer tube and the inner surface of the bushing. Because of the extremely high speeds involved in centrifugation, the oil film is heated substantially and a continuous flow water cooling system is provided for dissipating the heat transferred from the oil film to the bushing. Unfortunately, the heat generated within the oil film is also transferred to the rotary transfer tube causing heating of same, as well as heating of the sample solution flowing therethrough. However, many biological samples are adversely affected by heat, limiting the usefulness of continuous flow centrifugation.